A service contract is written around an assumed way of driving. When the car starts doing a different job, the use clauses matter more than the coverage list, because they decide whether the contract's terms still fit your situation.
Find the use clauses
Search the contract for the words towing, trailer, cargo, commercial, delivery, rideshare, off-road, racing, and modified. Each word may point to an exclusion, a notice requirement, or a condition attached to a claim. Some contracts state these terms in the exclusions. Others place them in a separate use or conditions clause. Read both places before you assume the contract is silent.
Ask what a change means
Put a few questions to the provider in writing. Ask whether a change in use voids the contract, whether it requires notice, and whether it changes coverage on particular parts such as the drivetrain or the cooling system. Keep the answers with the contract. Do not treat a verbal answer from a sales desk as settling the point, because the signed contract is the document that governs the claim.
Keep the record
Note the date and nature of the change, any written notice you sent, and the provider's reply. If you add a hitch or start hauling for work, record it in the same file you keep for service visits. When a claim comes in later, that file shows what you told the provider and when you told it, which is the kind of paper a dispute turns on.
Check the sample first
If you are still shopping, look for a contract you can read before you buy. Several providers on this site publish a sample contract, which lets you find the use clauses before you sign anything. The link below lists those providers so you can start there.
Find the sample contracts on the Vehicle service contract companies that post a sample contract you can read first page.